Arm device

ABSTRACT

Arm device adapted to move and position a first basic part (6) relatively to a second basic part (4), comprising at least three arms (1,2,3,7) capable of being extended and shortened in a controlled manner, said arms being free to pivot in attachments (5) on the second basic part, while one attachment on the first basic part is rigid, and one of said arms is torisonally rigid. A third basic part (15) is connected to the first basic part through a joint (16), and at least one auxiliary arm (12,13) is at one end connected to one of the arms (7) through a joint, while the other end of the auxiliary arm is connected to the third basic part (15), and the lengths of the auxilary arm can be varied. Thereby is achieved that the arm device has a large number of degrees of freedom with respect to movement of the third basic part, which holds a tool or a tool holder. Moreover, the tool or the tool holder may be journalled for rotation relatively to the third basic part ( 15).

BACKGROUND OF THE INVENTION

The present invention relates to an arm device adapted to move andposition a first basic part relatively to a second basic part, said armdevice comprising at least three arms capable of being extended andshortened in a controlled manner, and the arms are free to pivot intheir attachments on the second basic part, while one attachment on thefirst basic part is rigid, and one of the arms is torsionally rigid.Such a device is known from Norwegian acceptance print No. 148216. Asexamples of the use of such an arm device are mentioned industrialrobot, drilling rig for tunnels and mines, adjustment device foraerials.

As further examples of known technique are mentioned:

U.S. Pat. No. 3,215,391 shows an arm device capable of being used forfor instance adjustment of the position of an aerial, which, thus,constitutes one of the basic parts, while the other end of the arms isfastened to for instance a plate or similar, which may be stationary orfor instance fastened to a vehicle. The arms are rigidly attached ineach basic part, and are constituted by telescopic arms having universaljoints at the middle. This permits that one of the basic parts can pivotabout two of the universal joints relatively to the second basic part,and the pivotal movement is controlled by extension or shortening ofthat arm whose universal joint is not situated along the pivot axis.Moreover, it is possible to displace the basic parts parallelly to eachother, by extending and shortening the arms. Thus, the possibilities ofmoving the basic parts mutually are very restricted.

U.S. Pat. No. 3,374,977 shows a similar arm device, being adapted foraerial adjustment. The device comprises four arms being fastened withtheir ends to two basic parts. Said four arms, which can be extended andshortened and have universal joints at each end, have attachments at thecorners of equally large squares, and a fifth arm having a fixed lengthand universal joints at each end is fastened to the basic parts at thecenter of said squares.

The basic parts can be freely adjusted with respect to mutual direction,but the mutual adjustment is restricted, in that the fifth arm maintainsa fixed distance between the middle portions of the basic parts. Atleast two of those arms that are capable of changing their length mustbe actuated simultaneously. Moreover, the arm device is staticallyindetermined, and is not torsionally rigid, when the arms have equallengths.

U.S. Pat. No. 3,288,421 also shows an arm device adapted to move a basicpart relatively to another, and permits both a mutual angular adjustmentand parallel displacement. The device comprises six arms, and the endsof two by two arms are journalled in the same pivot point, whereby thearms stand in a zigzag pattern between the basic parts. The devicepresupposes that both of the basic parts have a relatively large area,and the number of arms is relatively large. The mutual movement of thebasic parts is very restricted.

Said Norwegian acceptance print No. 148216 shows a tool at the free endof the arm device. Said tool, which may of course be of a differentstructure than that shown in the print, is rigidly mounted on the firstbasic part, and can consequently only perform movements determined bythe movements of said basic part. For some applications thepossibilities of movement of the tool are too restricted. Said basicpart, and consequently also the tool, are rigidly connected to the endof one arm and can, therefore, only perform pivotal movements about theother basic part, about the pivotal mounting of said arm on the otherbasic part, possibly combined with movement towards or from the otherbasic part. In other words the tool always follows all the movements ofthe first basic part.

SUMMARY OF THE INVENTION

The object of the present invention is to achieve that the tool may alsobe moved relatively to the first basic part, at least in a tiltingmovement about one pivot axis, possibly about two pivot axes. Inaccordance with the invention this is achieved with an arm device asspecified in the succeeding claims.

The invention implies that the third basic part, and consequently alsothe tool, have four or five degrees of freedom with respect to movement.A sixth degree of freedom can be achieved in that the third basic partcan rotate relatively to the arm device. Thereby the tool can be broughtto any spatial position, within the limits determined by the dimensionsof the arm device and the possibilities of movement of the arms and theauxiliary arms, and the tool can be given any orientation in the space.Thus, an arm device has been achieved which theoretically givesunlimited possibilities of positioning tools.

For applications of the arm device in cases where it is essential toachieve as exact positioning as possible of the basic parts relativelyto each other the arm device can be equipped with means for measuringthe actual length of the arms, i.e. in such a manner that a possibleelastic extension or shortening of the arms due to the prevailing loadsis included in the measurement. The measured values can be compared withthe desired values, and corrections of the arm lengths can be performed.

The arms may for instance be hydraulic cylinders, and it is possible touse programmed control, as for known types of robots. The measuredvalues of the arm lengths can be fed to the control system, whichcontinuously performs corrections based on the measured values.

The arm device can be made with only three main arms, of which one mustbe able to transfer a bending moment. The same arm, or one of theothers, must be able to transfer torque. One arm, therefore, is rigidlyconnected to the first basic part, and the two portions of the arm whichcan be mutually shifted for varying of the length of the arm may beprevented from mutual rotation. The arm is fastened to the second basicpart in such a manner that it can pivot in all planes, but without beingable to rotate relatively to the second basic part. Alternatively saidarm may only be adapted to transfer bending movement, and not torque, asthe latter is transferred through another arm.

The arms may also be comprised of something else than cylinders andpiston rods, such as electrically driven arms, for instance according tothe solenoid principle or by means of a threaded rod which is screwedrelatively to a sleeve.

It is no absolute presupposition that the shortening and extension ofthe arms can be controlled within two extreme limits. An arm deviceaccording to the invention may also be utilized in such a manner thatone or more arms can merely perform their full stroke, i.e. that themovement cannot be stopped in any intermediate position. The arm devicemay then be used for instance for moving items between fixed points,whereby the mutual positions of the points are determined by the largestand smallest arm lengths.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the invention will be explained more detailed by meansof an embodiment, shown on the accompanying drawing. In the examplethose arms which are capable of being extended and shortened are shownas cylinders with piston rods, but as mentioned the arms can be madequite differently.

The drawing shows an embodiment with four arms between two basic parts.Three of the arms are capable of being extended and shortened, while thefourth arm, which is in rigid connection with one basic part, always hasa length which is determined by the other three arms, and, therefore,has no means for forced variation of the length. Moreover, the fourtharm is torsionally rigid.

DESCRIPTION OF PREFERRED EMBODIMENTS

The arm device shown comprises three arms 1,2,3 provided mainly in thecorner edges of a pyramid. These three arms are fastened with one end toeach basic part 4,6 through ball joints or universal joints 5, and eacharm can be extended and shortened. Moreover, the arm device comprises afourth arm 7. The arm 7 is fastened to the basic part 4 through auniversal joint 5, while the other end of the arm 7 is rigidly connectedwith the basic part 6. In addition the arm 7 can transfer torque. Thisis indicated in that the rod portion of the arm is splined, whereby thesplines are guided in corresponding recesses in the cylinder portion.The arm 7 is not connected to any system for forced variation of thelength, because the length of the arm alone is adapted to the lengthvariations of the other arms 1,2 and 3.

Moreover, the arm device may be equipped with not shown means forindicating the actual length of the arms 1,2 and 3.

The arm 7 will transfer both bending moments and torque. The arms 1,2and 3 are only able to be exposed to tension and pressure, and measuringor indicating of the actual arm length, therefore, gives an unambiguousexpression of the position of the tool relatively to the basic part 4 orof the relative position of the two basic parts 4 and 6.

The arm being capable of transferring torque may have the function ofpreventing mutual rotation of the basic parts, but may also be used tocause a controlled mutual rotation of the basic parts. Such rotation ispossible due to the joints at each end of the other arms, and mutualrotation of the basic parts can be performed to such an extent (rotationangle) that the arms are obstructed by each other. Thus, the rotationangle can be very large. During such rotation the basic parts will,provided that the lengths of the arms which have joints are heldconstant, approach each other progressively on both sides of a normalposition where the distance between the basic parts is at a maximum. Ifthe rotation starts when the arms are somewhat shortened the distancebetween the basic parts can be held constant during the rotation, bygradually extending the arms. The arm causing the rotation will take thenecessary length at any moment.

There are several possibilities of transferring the torque necessary forsuch rotation. A servomotor may for instance be provided in one of thebasic parts, in order to rotate the end of the arm being capable oftransferring torque relatively to the respective basic part. The mutualrotation may also take place in the arm proper, in that means areprovided for controlled mutual rotation of two arm portions.

In the embodiment shown such rotation as mentioned above can be carriedout for instance in that the thick portion of the arm 7 contains aservomotor which can rotate the thin portion of the arm relatively tothe thick portion, so that the basic part 6 rotates relatively to thebasic part 4. The rotation angle will be limited by mutual contactbetween the arms 1, 2 and 3.

The above described arm device corresponds to the arm device appearingfrom Norwegian acceptance print No. 148216.

In the example shown there are, between the arm 7 and a third basic part15, provided auxiliary arms 12 and 13. The third basic part 15, beingmerely shown diagrammatically in the form of a cylinder, is fastened tothe basic part 6 by means of a joint 16, being a hinge or a ball jointor universal joint, and in the example the auxiliary arms 12 and 13 arefastened through supports 8,9 and 10,11 to the arm 7 and the third basicpart 15, respectively. The auxiliary arms 12 and 13 are telescopic andare connected to the supports 8,9,10 and 11 through joints, and thelengths of the auxiliary arms can be adjusted. It will be appreciatedthat all the supports 8,9,10 and 11 will follow the movements of the arm7 as long as the auxiliary arms 12 and 13 have constant lengths. Therebythe movements of the third basic part 15 are determined merely by thearms 1,2,3 and 7. In addition extension and shortening of the arms 12and 13 cause tilting movement of the third basic part about the joint16.

The third basic part, and hence the tool, has five degrees of freedomfor movement. A sixth degree of freedom can be achieved in that the tool14 can rotate relatively to the third basic part 15, which is showndiagrammatically as a short cylinder, while the tool 14 is showndiagrammatically as an elongate, thinner cylinder.

In the embodiment shown the arm 7 is inverted relatively to the arms 1,2and 3. This is merely due to practical reasons when the arms areconstituted by cylinders having pistons and piston rods. The provisionof the cylinders of the arms 1,2 and 3 nearest to the basic part 4implies that the mass of the moving parts is small and that thecylinders take up space where most space is available. The arm 7 has itscylinder nearest to the third basic part 15 because it is mostappropriate to mount the supports 8 and 9 on a cylinder rather thanmounting them on a substantially thinner piston rod.

The invention can be materialized with only one auxiliary arm, providedthat the joint 16 is a hinge joint having only one pivot axis. This,however, reduces the number of degrees of freedom.

Under all circumstances the joint 16 must be capable of transferringtorque, because the third basic part 15 must not be able to pivot freelyrelatively to the first basic part 6.

I claim:
 1. Arm device adapted to move and position a first basic part(6) relatively to a second basic part (4), comprising at least threearms (1, 2, 3, 7) capable of being extended and shortened in acontrolled manner, one end of each of said arms being free to pivot inattachments (5) on the second basic part, the other end of each of saidarms being attached to said first basic part with the attachment of oneof said arms to the first basic part being rigid, and one of said arms(7) is torsionally rigid, characterized in that a third basic part (15)is connected to the first basic part (6) through a joint (16), and thatat least one axiliary arm (12, 13) of positively and controllablyadjustable length is connected to and arranged to be movable in itsentirety with said other end of said torsionally rigid arm through ajoint, while the other end of the auxiliary arm is connected to thethird basic part (15), which is adapted to hold a tool (14).
 2. Armdevice as claimed in claim 1, including two auxiliary arms (12,13), andthat said joint (16) is a ball joint or universal joint.
 3. Arm deviceas claimed in claim 1, including one auxiliary arm, and that said joint(16) is a hinge joint having one pivot axis.
 4. Arm device as claimed inclaim 1, characterized in that said tool (14) or a tool holder isjournalled for rotation relative to the third basic part (15).